This invention relates to a method for producing a plurality of fiber glass strands into an improved bundle of strands. More particularly, this invention relates to a method for producing an improved fiber glass roving.
In conventional production of glass fibers, the glass fibers are made from a multitude of fine glass filaments, which are formed by being drawn at a high rate of speed from molten glass streams flowing from small openings in a bushing, which contains molten glass. Since glass fibers easily abrade each other, a chemical size is applied to the filaments to protect the filaments when they are gathered together into a strand, and when the strand is subjected to further processing. The chemical size gives the filaments integrity and workability for any standard textile or reinforcement use. After the glass filaments are formed and coated with the chemical size, they are drawn together by a gathering shoe into one or more glass fiber strands. The drawing of the filaments from the bushing is effected by the use of a winder is also used to wrap to wrap the strand on a tube or spool to produce a forming package. The glass fiber strand is removed from the forming package to produce the main fiber glass products such as mats, rovings, woven rovings, (also called roving cloth), chopped and milled fibers, and yarns.
Rovings have been defined as cylindrically shaped packages of bundles of glass fiber strands wound up in parallel without a twist. Rovings are made placing a number of forming packages on a creel and collecting the strands together and passing them through guide eyes and tensioning devices and then winding the strands together as one bundle of strands onto a winding machine that is standard in the industry.
In the conventional production of glass filaments or fibers into bundles or strands to be processed into roving, it is customary to use only the size or binder material which is placed on the filaments as they are formed under the bushing and gathered into strand. The size or binder material on the strand provides some degree of integrity or bonding for the filaments when the strands are gathered in the roving process. Rovings produced in this manner are referred to as dry rovings.
Glass fiber rovings are further processed by chopping or weaving the rovings for use in many different applications. When the rovings are chopped, the chopped glass fibers are combined with resin or binders for lay up methods of molding or to form preforms or for the manufacture of sheeting. When the rovings are woven, they are used as reinforcing materials for resins such as polyesters or epoxides. Rovings have also been used for winding and rod making, for example, in the manufacture of pipe and cylindrical tanks.
When rovings are chopped, the glass fiber strands in the roving must have good choppability, which is controlled by such factors as the diameter of the strand, the fiber size used during formation of the strand, the drying time of the forming package and the effect of additives in the sizing composition. Good chopping characteristics of the strand include good integration of the filaments in the strand so they do not readily filamentise, and therefore, slip easily over one another as they hit a surface after chopping. The preservation of strand integrity during chopping is important as this facilitates the removal of air during molding. But at the same time the roving must have the characteristic that after it is chopped the chopped strands do not stick to one another.
In producing rovings for weaving, the bundle of strands should be slightly stuck together, so that the roving enters the cloth manufacturing machinery in such a manner that the strands are stuck together, but the roving comes out in the cloth so that the strands are no longer stuck together. This facilitates impregnation of the cloth with liquid resins.
The rovings particularly useful in the above described methods of chopping and weaving are the dry rovings, and although these rovings have adequate choppability characteristics they do not possess all of the characteristics desired for good choppability. Roving of glass fibers or filaments in a dried condition are not adequately held together, where several rovings are combined into a single roving, and this is probably because of fracture of the size or bond during processing. When a dried, sized roving is chopped in a cutting device, only partial cutting takes place and usually a large number of filaments in the roving are not severed, because they readily separate when contacted by the cutter or severing device.
The prior art has confronted this problem by conditioning or treating the roving with moisture before or after the strands of the roving are wound in a package. This treating or conditioning of the roving prior to further processing involves contacting the roving with water or other vaporizable liquids so that the roving, while in wet condition, may be satifactorily severed into short lengths, or combined with other rovings to form a multiple assembly roving, or subjected to other processing steps. Conditioning the glass fiber strands with moisture or a vaporizable liquid can lead to problems of binder rub off during further processing. The binder rub off would cause additional tension and would cause problems in doffing the roving package from the winder.
Also some rovings for use in chopping have the strands of the roving stuck together in a manner which is referred to as taping. As described in "The Manufacturing Technology of Continuous Glass Fibers," by K. L. Loewenstein, Elsevier Scientific Publishing Company, New York, 1973 at page 260, taping is an important characteristic in order to present a consolidated bundle rather than individual strands while passing the roving through eyes and guides of the loom. For rovings constituting the warp in cloth this is of smaller importance; for rovings to be used in the weft, it is very important in order to avoid intolerable amounts of broken glass fibers being transferred to the atmosphere. Taping is carried out by heating the complete roving in an oven at about 100.degree.-110.degree. C. for four-six hours depending on the size of the roving. Taping or ribbonization, as it is sometimes called, is effected by the size or binder that is placed on the glass fibers during forming. This size or binder on the glass fiber strands that are made into roving provides some adhesion between the glass fiber strands in the roving after the roving is heated in the oven. Taping provides a degree of integrity between the strands in the roving but this degree of integrity could be improved upon to give better choppability and processability to the roving.
It is an object of this present invention to provide a method for producing bundles of strands having integrity between the strands to hold the strands together temporarily and to allow better processability by depressing fraying and snagging of the strands on processing machinery. It is an additional object of the present invention to provide a method for producing roving having integrity between the strands so that the strands are held together temporarily to increase the choppability of the roving, but once the roving is chopped the strands are no longer held together.
It is an additional object of the present invention to provide a method for producing roving which has improved integrity between the strands so that the strands are held together temporarily when the roving enters a cloth manufacturing or weaving machine but permits the strands to separate in the cloth or woven product exiting from the machine.